The following relates generally to wireless communication, and more specifically to synchronization signal block signaling for wireless communications in shared spectrum.
Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems, (e.g., a Long Term Evolution (LTE) system, or a New Radio (NR) or 5G system). In some examples, wireless multiple-access communications system may include a number of base stations or access network nodes, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE). In a LTE or LTE-Advanced (LTE-A) networks, a set of one or more base stations may define an eNodeB (eNB). In other examples (e.g., in a NR or 5G network), a wireless multiple access communication system may include a number of smart radio heads (RHs) in communication with a number of access node controllers (ANCs), where a set of one or more RHs, in communication with an ANC, defines a base station (e.g., an eNB or gNB). A base station may communicate with a set of UEs on downlink (DL) channels (e.g., for transmissions from a base station to a UE) and uplink (UL) channels (e.g., for transmissions from a UE to a base station).
A base station and a UE may exchange various messages during a cell acquisition procedure to establish a communication link. In some cases, a base station may utilize beamformed transmissions during the cell acquisition procedure to mitigate path losses (e.g., if the base station is communicating at higher frequencies). A UE that includes multiple antennas may receive transmissions from a base station using various antenna configurations to determine a transmission beam and antenna configuration suitable for future communications. In shared or unlicensed radio frequency spectrum, some regulated domains require base stations to perform channel sensing before accessing the channel. The base station performs a clear channel assessment (CCA) to determine a time to transmit in the shared or unlicensed radio frequency spectrum. This results in asynchronous transmissions across multiple base stations.
In some cases, a UE may perform an initial access (or initial acquisition) procedure to gain access to a wireless network. As part of the initial access procedure, the UE may search for a synchronization channel transmitted by a network access device, such as a base station, of the wireless network. The UE may be configured to periodically listen for a synchronization channel from the base station. UEs operating in licensed radio frequency spectrum bands may combine multiple received synchronization signal (SS) blocks of a synchronization channel to demodulate the received signal. UEs operating in a shared radio frequency spectrum band, such as an unlicensed radio frequency spectrum band, may be unable to combine multiple SS blocks due to the asynchronous nature of shared radio frequency spectrum band transmissions. As such, UEs operating in shared radio frequency spectrum bands may perform single-shot detection and demodulation of a single received SS block. Existing systems do not provide a mechanism for UEs to reliably perform single-shot detection and demodulation of SS blocks.